Abstract
We observe significant dust-correlated emission outside of H II regions in the Green Bank Galactic Plane Survey (-4? < b < 4?) at 8.35 and 14.35?GHz. The rising spectral slope rules out synchrotron and free-free emission as majority constituents at 14 GHz, and the amplitude is at least 500 times higher than expected thermal dust emission. When combined with the Rhodes (2.326 GHz) and Wilkinson Microwave Anisotropy Probe (23-94 GHz) data, it is possible to fit dust-correlated emission at 2.3-94 GHz with only soft synchrotron, free-free, thermal dust, and an additional dust-correlated component similar to Draine & Lazarian spinning dust. The rising component generally dominates free-free and synchrotron for ? 14?GHz and is overwhelmed by thermal dust at ? 60?GHz. The current data fulfill most of the criteria laid out by Finkbeiner and coworkers for detection of spinning dust.
Highlights
The statistical detection of anomalous dust-correlated emission, far brighter than expected thermal dust emission at $10– 30 GHz, has been well established (COBE, Kogut et al 1996; Saskatoon, de Oliveira-Costa et al 1997; Owens Valley Radio Observatory [OVRO], Leitch et al 1997; 19 GHz survey, de Oliveira-Costa et al 1998; Tenerife, de Oliveira-Costa et al 1999)
Even though Foreground X could be ubiquitous, severe limitations in previous data sets have prevented a convincing detection over a large solid angle. Surveys such as the 19.2 GHz survey (Cottingham 1987; Boughn et al 1992) and the Tenerife survey (Gutierrez et al 2000) have such large beams (3 and 5 FWHM, respectively) that any diffuse interstellar medium (ISM) emission in the plane is confused with H ii regions, and, even when it can be detected by spectral slope, there are relatively few independent pixels in the data showing rising emission
Another emission mechanism that could produce Foreground X is magnetic dust (Draine & Lazarian 1999). This mechanism has nothing to do with rapid rotation of magnetic dipoles; rather, it results from the thermal fluctuations in the grain magnetization, yielding an additional thermal emissivity mechanism
Summary
The statistical detection of anomalous dust-correlated emission, far brighter than expected thermal dust emission at $10– 30 GHz, has been well established (COBE, Kogut et al 1996; Saskatoon, de Oliveira-Costa et al 1997; Owens Valley Radio Observatory [OVRO], Leitch et al 1997; 19 GHz survey, de Oliveira-Costa et al 1998; Tenerife, de Oliveira-Costa et al 1999). Surveys such as the 19.2 GHz survey (Cottingham 1987; Boughn et al 1992) and the Tenerife survey (Gutierrez et al 2000) have such large beams (3 and 5 FWHM, respectively) that any diffuse ISM emission in the plane is confused with H ii regions, and, even when it can be detected by spectral slope (as in the Tenerife data at 10 and 15 GHz), there are relatively few independent pixels in the data showing rising emission Other experiments, such as the COBE Differential Microwave Radiometer (DMR; 7 FWHM), observed at higher frequencies at which the spinning-dust spectrum is expected to roll off and cannot be separated from free-free by spectral slope or spatial resolution. Additional data from Rhodes and WMAP (smoothed to 1 FWHM) are analyzed in x 5, and conclusions are stated in x 6
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